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8/2/2019 Tests of Soil and Bitumen
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MATERIAL TESTING AND THEIR SIGNIFICANCE
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Soil1.Grain Size Analysis2.Atterbergs Limit3.Compaction Test4.Free Swell Index5.Direct Shear6.
California Bearing Ratio
7.Tri-Axial Compression Test
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Grain Size Analysis(IS 2720: part 4)
PURPOSE
The commonly used properties for classification of soil are the grain
size distribution and atterbergs limits which are also used to determine
the suitability of soil as a sub-grade material and other purposes.
The soils are generally divided into four groups based on their particle
size Gravel: coarser particles of rock and sand between 80mm and
4.75mm
Sand: smaller fraction of particles between 4.75mm and 75micron Silt: soil fractions smaller than 75 micron are called fines which
consist of silt and clay.75 micron to 2 micron is silt
Sand: microscopic and sub-microscopic particles lower than 2micron is clayey particles.
Dry sieve analysis is generally carried out on coarse aggregates or sandy
soil either retained or passing through 4.75 mm sieve if they are
cohesion less and without lumps. Otherwise wet sieve analysis is
conducted.
Wet sieve analysis is carried if the sample contains cohesive lumps and
it is not possible to break them into their respective grain size by any
pulverizing methods. Soils with fractions which are likely to causeflocculation are added with 2 gm of sodiumhexameta-phoshate or 1 gm
of sodium hydroxide / sodium carbonate as a dispersing agent and left
for soaking.
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Uniformity coefficient U, is expressed as (D60 /D10 ), where D60 and D10
are particle size corresponding to 60 % and 10% fines in the grain size
distribution curve. A high value of uniformity coefficient such as U
greater than 4 or 5 indicates the presence of wide range of particle sizeor soil is well graded. A low U of the order of lower than 2 indicates
uniformly graded soil
Soil classification
Ordinarily sieve analysis (dry/wet) will be quite sufficient along with the
tests for consistency limits for identifying and classifying soil.
Proportioning soils for mixed designThe principle of mechanical soil stabilization is to mix two or more
number of selected soils and gravels or aggregates in a suitable
proportion that a desired grain size distribution is obtained for the
combined materials as per mix design
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ATTERBERG`S LIMIT(IS 2720 PART 5 & 6)
PURPOSE
The physical properties of fine grained soils, especially of clayey soils
differ considerably at different water contents present in soil. The tests
for determination of consistency limits are all empirical.
Liquid Limit: It is defined as the minimum water content at which the
soil will flow under the application of a very small shearing force.
Plastic Limit: It is defined as the minimum water content at which soil
remains in a plastic state and posses moulding characteristics.
Shrinkage Limit: it is defined as the maximum water content at which
further reduction in water content does not cause reduction in volume.
LIQUID LIMIT TEST (By cone penetration one point method)
In the case of soils whose liquid limit exceeds by 120% in case of one
point method mechanical method should be used.
PRINCIPLE
Since the depth of penetration is in an indirect reflection of shear
strength at different water contents, it has been found, within the
framework of a scientific base that W/WL against logD or D is unique
and is independent of soil type. The resulting linear relation enables to
determine liquid limit water content at specified penetration of 20 mm
depth.
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CALCULATION
The water content is determined for any accepted trial and the liquid
limit water content is calculated by any one of the following
relationships.
WL = WN / 0.77 LogD
WL = WN / (0.65 + 0.0175 D)
The liquid limit of the sample shall be reported to first decimal place
and history of the sample that is natural state, oven dried, or any
pretreatment done should be mentioned.
Shrinkage Limit of remoulded sample, Ws = w (v- vo/wo)100
where
Ws = shrinkage limit in percent,
w = moisture content of wet soil pat
V = volume of wet soil pat in ml,
Vo = volume of dry soil pat in ml, and
Wo - weight of oven-dry soil pat in g.
Application of consistency limits
Identification and classification of soils
Compressibility
Plasticity index
Application of data in the construction of highway material
Group index method of classifying sub grade soil
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COMPACTION TEST
PURPOSE
Compaction of a soil is a mechanical process by which the soil particles
are constrained to be packed more closely together by reducing air
voids. Soil compaction decreases air voids and consequently increases
dry density. This may result in increase in shear strength. The possibility
of future settlement or compressibility decreases and also the tendency
for subsequent changes in moisture content decreases.
Light compaction is done filling the mould in three equal layers and
compacted by 2.6 kg hammer with 25 blows in small mould and 55
blows in large mould of 150 mm diameter
Heavy compaction is done by filling the mould in 5 layers and
compacting by 4.9 kg hammer with 25 blows each in small mould of
100 mm diameter and 55 blows in large mould of 150 mm diameter.
RESULT
Moisture- dry density graph is plotted with moisture content on the X
axis and dry density on Y axis and a smooth curve is drawn connectingthe points, which is called compaction curve.
From this curve, the maximum density is noted and the corresponding
value of moisture content is taken as optimum moisture content OMC
DISCUSSION
The objective of the compaction test is to determine the relationship
between compacting moisture content and dry density achieved for the
soil keeping the compacting energy per unit volume constant.
Therefore to increase the accuracy of results the volume to be struck
off from the collar should not be very different in each case and it
should be like 6 mm of soil should be there after removing the collar to
be struck off to get good reproducibility.
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APPLICATION OF COMPACTION TEST
In field compaction the compacting effort is first controlled at OMC and
the adequacy of compaction is checked by checking the dry density
achieved
The results are used for quality control in the construction of
pavements as IRC and MORTH recommends achieving 97% of the dry
density achieved in heavy compaction in sub-grade layer and 95% in
compacted embankments.
Suitability of the soil to be used in highway work is based on the
specified minimum value of dry density achieved in compaction test. As
per MORTH for deciding suitability of soil to be used as sub-grade, themaximum dry density should not be less than 1.75 g/cc
The maximum dry density indicates the strength property of the soil,
lower the dry density it indicates weaker is the soil although it is just
qualitative idea quantification is done by conducting strength tests.
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SHEAR TESTS ON SOILS(IS 2720 part 11, 12, 13)
PURPOSE
The strength parameters namely the cohesion and the angle of internalfriction or shearing resistance of soils are usually found from the shear
tests. Two commonly used methods are direct shear test and triaxial
compression test
DIRECT SHEAR TEST
In this test the soil specimen is placed in the shear box between two
halves and a normal load is applied. Then a longitudinal displacementor the shear force is applied and its magnitude is increased until the
specimen fails along the predetermined horizontal plane between the
two halves of shear box
By repeating the direct shear test at different magnitudes of normal
load, a graph is plotted with normal stress values on the X-axis and the
shear stress values on Y-axis. The value of cohesion C, and the
magnitude of angle of internal friction are obtained from the graph
DISCUSSION
The main advantage of direct shear test is its simplicity and less time
consuming in comparison to tri axial. But it is also associated with some
disadvantages as follows
The failure is forced to take place along pre determined horizontalplane not the weakest plane
The area of cross section of specimen progressively decreases during
the test.
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There is no uniform shear stress distribution within the failure plane
and drainage conditions are not controlled
TRI-AXIAL COMPRESSION TEST
In triaxial test the load applied is mostly transient and it is carried out
on the soil having more cohesive properties
APPLICATIONS
The shear strength parameters C and internal friction can be found and
thus shearing resistance can be found out
Elastic modulus values or modulus of deformation values of sub grade
and other pavement layer materials are determined from tri axial test.
The unconfined compression test is considered to be the special case in
which lateral confining pressure is zero.
FREE SWELL INDEX
PURPOSE
Free swell index is conducted on soils which have the potential to swell.
It is desirable to carry out further detailed investigations on soils with
high free swell index.
DISCUSSION
The volume of the soil sample in the jar is noted as Vk and water as Vw
than FSI = 100* (Vw - Vk )/Vk
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CALIFORNIA BEARING RATIO
PURPOSE
The CBR test denotes a measure of resistance to penetration of a soil orflexible pavement material of standard plunger under controlled test
conditions. It is a method for evaluating the strength of sub grade soil
and other pavement materials for the design and construction of
flexible pavements.
DISCUSSION ON RESULTS
The CBR values at 2.5 and 5.0 mm penetration levels are calculated foreach specimen from the corresponding graphs. Generally the CBR value
at 2.5 mm penetration is higher but if the value is higher at 5.0 mm
than test is repeated and If still it is higher than higher value is adopted.
The initial concavity of the load penetration curve calling for the
correction may be due to one or more of the following reasons:
The top layer of soaked soil specimen is too soft or slushy after soakingin water.
The top surface of the specimen is not even.
The penetration plunger of the loading machine is not vertical result in
bottom surface of plunger not being horizontal and fully in contact with
the top surface of specimen.
APPLICATIONS
Based on CBR data collected, empirical design charts were developed
by the California state highway department, correlating the CBR value
and pavement thickness requirement.
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AGGREGATES1.Aggregate Impact test2.Los Angeles Abrasion test
3.Specific gravity and water absorption test
4.Shape test
5.Soundness test
6.Stripping value test
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Aggregate Impact test(IS 2386 Part 4)
PURPOSE
Toughness is the property of the material to resist impact. During the
construction process of pavement layers, particularly compaction by
heavy rollers and also due to movement of heavy wheel loads of traffic,
the road aggregates are subjected to impact therefore stone aggregates
should therefore be sufficiently tough to resist fracture under impact
loads.
DISCUSSION
Aggregate impact value test of a sample not only depends on
toughness and strength parameters it also depends on the shape
factors such as flakiness and elongation of the aggregates
APPLICATION
The aggregate impact test is considered to be an important test to
assses the suitability of the aggregated as regards the toughness for usein various constructional purpose mainly highway.
RESULTS
It is expressed as percentage of finer material passing 2.36 mm IS sieve
after test to original weight.
Aggregate impact value Toughness property
Less than 10 Exceptionally strong/tough
10 to 20 Very tough
20 to 30 Good for pavement construction
Above 35 Weak for pavement construction
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LOS ANGELES ABRASION TEST(IS 2386 part 4)
PURPOSE
Due to movement of traffic, the road stones are used in the surfacingcourse of pavements are subjected to wearing action at the top surface.
Resistance to wear or hardness is hence a essential property for road
aggregates especially when used in wearing course. Thus road stones
should be hard enough to resist the wearing under heavy traffic loads.
RESULT
The result is expressed as a percentage wear and the average value of
the two test. Percentage wear is the amount of fines to the originalweight passing through 1.70 mm IS sieve
DISCUSSION
Los angeles test is very commonly used to evaluate the quality of
aggregates for use in pavement construction, especially to decide
hardness of aggregate M
Maximum allowable los angeles abrasion value of aggregates given by
MORTH for different layers is given in the tableTypes of pavement layer Los angeles abrasion value,
maximum
WBM sub-base, WBM, WMM and
CRM base course
40Bituminous macadam and binder
course
Dense graded bituminous
macadam binder
Dense graded bituminous
macadam binder course 35
Cement concrete pavement
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SPECIFIC GRAVITY AND WATER ABSORPTION(IS 2386 PART 4)
PURPOSE
The specific gravity of an aggregate is considered to be measure ofstrength or quality of the material. Stone having low specific gravity are
generally weaker than those with higher specific gravity values. The
specific gravity is made to use in weight-volume conversions.
CALCULATION
Specific gravity, apparent specific gravity and water
Absorption shall be calculated as follows:
Specific gravity= (dry weight of aggregate)/(weight of equal volume of
water)
Water absorption (percent of dry weight) = % by weight of water
absorbed in terms of oven dried weight of aggregates
DISCUSSION AND APPLICATION
The water absorption test does not always gives reproducible results inaggregates with high porosity.
The specific gravity of coarse aggregates used in road construction
ranges from 2.5 to 3.2 with an avg value of 2.70.
Water absorption is accepted as measure of its porosity. Sometimes
this value is even considered as a measure of its resistance to frost
action though not has been confirmed by adequate research.
Water absorption of about 0.1 to 2.0 percent for coarse aggregates
normally used in road construction.
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SHAPE TEST(IS 2386 part 1)
PURPOSE
The shape of aggregate particle is determined by the percentage of
flaky and elongated particles contained in it. Presence of flaky particles
in the construction is undesirable as they may cause weakness with
possibilities of breaking down under loads.
APPLICATION
In the road construction work MORTH has specified the limits of
flakiness index and elongation index. Though elongated shape of
aggregates also gets broken down under heavy rollers duringcompaction and also during compaction under heavy traffic load.
MORTH has specified the maximum permissible value of combined
flakiness and elongation index of coarse aggregates as 30% for WMM
base course and other
SOUNDNESS TEST
(IS 2386 PART 5)PURPOSE
Soundness test is intended to study the resistance of course and fine
aggregates to weathering action. In the absence of adequate
information the laboratory test simulation accelerated weathering
condition is carried out to judge the durability or the soundness of the
course aggregates.
DISCUSSIONIf the sample contains less than 5% of any of the sizes specified under
procedure that size should not be tested, but for the purpose of testing
it shall be considered to have the loss in sodium sulphate or magnesium
sulphate treatment as the avg of next smaller or next greater size
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APPLICATION
The soundness test is useful to asses the resistance of the aggregates to
weathering. For cement concrete likely to be exposed to the action of
frost, coarse, and fine aggregates should pass an accelerated soundness
test. As a general rule, it may be taken that the avg loss of weight after
10 cycles should not exceed 12% with sodium sulphate and 18% with
magnesium sulphate
Indian road congress has specified maximum permissible loss in weight
in soundness test after 5 cycles as 12% with sodium sulphate and 18%
with magnesium sulphate for the aggregates to be used in bituminous
binder course and surfacing of road pavements.
STRIPPING VALUE(IS 6241)
PURPOSE
Stripping of coated binder or detachment of a portion of bitumen
coating from the aggregate due to the presence of water. So to
measure and deal with this problem test is conducted to calculate
stripping value. The stripping is due to the fact that those aggregateshave higher affinity towards water than bituminous binders and this
displacement of bituminous coating from the aggregates depends on
the physio-chemical forces acting on the system. Most road aggregates
are electrically charged for example silica, a common constituent of
igneous rock posses a weak negative charge and hence have a higher
affinity for polar compounds like water
DISCUSSIONThe stripping value is the ratio of uncovered area observed visually to
the total area of aggregates in each test, expressed as percentage.
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BITUMEN1.Penetration Test
2.Ductility Test
3.Viscosity Test
4.Softening Point Test
5.Flash and Fire Point Test
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PENETRATION TEST(IS 1203)
PURPOSE
Determination of absolute viscosity is not so simple therefore theconsistency of these materials are determined by indirect methods.
Penetration test is indirect method to determine consistency by
measuring the depth to which a standard needle will penetrate
vertically under its own weight. Thus the basic principle of the
penetration test is the measurement of the penetration.
DISCUSSION
It may be noted that the penetration value is influenced by anyaccuracy as regards of following factors
Pouring temperature, size of needle, weight placed on needle, test
temperature, duration of releasing the penetration needle, period of
cooling etc.
APPLICATION
It is most commonly adopted test to determine the grade of the
material in terms of its hardness.Penetration test is empirical test and there is no direct relation to the
fundamental properties of binder.
DUCTILITY TEST(IS 1208)
PURPOSE
It is desirable that the bitumen binders used in the bituminous mixes
form ductile thin films around the aggregates. The binder material
which posses sufficient ductility would crack and thus provide pervious
pavement surface
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DISCUSSION
The ductility value gets seriously affected if any of the following factors
are varied
1.Test temperature2.Pouring temperature3.Diameter of briquette, particularly the cross section at the
minimum width should be 10x10 mm
4. Improper level of briquette placement or the stretched thread ofspecimen touching the top or bottom surface of water bath
5.Rate of pulling6.Period of cooling
APPLICATIONS
A certain minimum ductility is considered essential because of the temp
change in the bitumen mix and the repeated deformations that occur. If
the bitumen is low in ductility pavement may crack and lead to failure.
VISCOSITY TEST(IS 1206 PART I, II, III)
Viscosity of a liquid is the property that retards its flow due to internal
friction and it is a measure of resistance to flow of the liquid. The
viscosity is of two types as
ABSOLUTE VISCOSITY: the ratio between the applied shear stress and
the rate of shear is called the absolute viscosity measured in poise.
KINEMATIC VISCOSITY: it is the ratio of the absolute viscosity to the
density of the liquid, both at the same temperature measured instokes.
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APPLICATIONS OF ABSOLUTE AND KINEMATIC VISCOSITIES
Previously grading of bitumen is done as per the penetration test but
now more rational methods are available to categorize bitumen
material known as VISCOSITY GRADING (VS)
SOFTENING POINT TEST(IS 1205)
PURPOSE
Bitumen does not suddenly change from solid to liquid state, but as the
temperature increases it becomes softer until it flows readily.the
softening point is the temperature at which the substance attains
particular degree of softening under specified condition of test. And asall bitumen mixes are required to be soft and flowable so as to make
possible their mixing with aggregates
DISCUSSION
To ensure the credibility of the test the following conditions should be
taken care of:
1.Quality and type pf liquid in the bath2.Weight of balls3.Distance between bottom ring and bottom base plate4.Rate of heating
APPLICATIONS
Softening point thus gives an idea of the temperature at which the
bituminous material attains a certain viscosity. Bitumen with higher
softening point may be preferred in warmer places.it is also used to
sometimes specify hard bitumens and pitches
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FLASH AND FIRE POINT TEST(IS 1209)
PURPOSE
Flash point test gives an indication of the critical temperature at andabove which suitable precautions should be taken while heating the
bitumen.
FLASH POINT: it is the minimum temperature at which bituminous
binder starts emitting the volatile vapours and these volatile vapours
can momentarily catch fire though the binder does not burn itself.
FIRE POINT: on further heating it is the lowest temperature at which
application of test flame causes the binder material to ignite and burn
atleast for 5 seconds under specified conditions.
Recommended